According to the optical theorem, there is a nonzero relative phase
between \(G_E\)  and \(G_M\) .
At \(M_{\Lambda \bar{\Lambda }} = 2.396\)  GeV, where we have
the largest \(\Lambda \bar{\Lambda }\)  sample of 555 events
from 66.9 pb\(^{-1}\)  data, a multidimensional analysis
was used to make a full determination of the \(\Lambda \) 
electromagnetic form factors for the first time for any baryon;
the relative phase difference is
\(\Delta \Phi = 37^\circ \pm 12^\circ \pm 6^\circ \)  [1]}
with the input parameter \(\alpha _\Lambda = 0.750\pm 0.010\) 
measured from \(J/\psi \)  decays [2]}.
The improved determination of \(\alpha _\Lambda \)  also has profound
implications for the baryon spectrum, since fits to such observables
by theoretical models are a crucial element in determining
the light baryon resonance spectrum, which provides a point of
comparison for theoretical approaches [3]}.
The \(|G_E/G_M|\)  ratio was determined to be
\(R = 0.96 \pm 0.14(\rm stat.) \pm 0.02(\rm sys.)\)  and
the effective form factor at \(M_{\Lambda \bar{\Lambda }} = 2.396\)  GeV
was determined to be
\(|G_{eff}| = 0.123 \pm 0.003 (\rm stat.) \pm 0.003 (\rm sys.)\) .
The \(\Lambda \)  angular distribution and the polarization
as a function of the scattering angle are shown in
Fig. REF (a) and (b), respectively.
This first complete measurement of the hyperon electromagnetic
form factor is a milestone in the study of hyperon structure,
while the long-term goal is to describe charge and magnetization
densities of the hyperons.
<FIGURE>